04-04-2020, 04:49 AM
(04-03-2020, 11:17 PM)danbrotherston Wrote: SARS (v1?) died out, because everyone who was sick with it got better or died, and there were no new patients, thus the virus died out (of the human population anyway). The key to doing this is controlling the R0. This is much harder for a virus like SARS-CoV-2 because it's R0 is much higher to begin with (for various reasons including pre- and a-symptomatic transmission), but it is still possible to get R0 under 0 and thus starve the virus of new hosts. China has already (or at least claimed to have) done this in specific areas.
If you can do this in a local area then you can shrink the infected population then reduce restrictions while controlling new cases through tracing, testing, travel restrictions, and quarantining, you can be free of a virus, even without herd immunity. In theory at least--I think we're yet to see if this is possible in practice with this virus but the short answer is no, it's not necessarily the case that everyone must get the virus before herd immunity is acquired.
Yes, eradication is NZ's Plan A. That would require incoming travellers to do self-isolation so it wouldn't be good for the tourism industry but it's better than lockdown. They have been talking a bit about Plan B but that's not clear. The increase has been about 80 for a few days now and might go down next week if things go well, although there certainly has been some community transmission.
I think we got rid of the original SARS and MERS this way. They had more favourable conditions as well.
(04-03-2020, 11:17 PM)danbrotherston Wrote: It's also not necessarily the case that "everyone getting it" would actually provide protection either, this virus does mutate, and while I think experts haven't seen it mutate sufficiently to avoid new immunity (nor do experts even know how long or effective acquired immunity is for this virus), it's entirely possible that it could mutate in that way in the future, just as the flu and cold viruses do every year. In fact, again, I'm not an expert, but I believe that everyone getting it, would make it more likely that it would mutate in that way.
I don't think we'd see 100% infection rates (which would be catastrophic, although less than 1918), but getting to 60% would slow down spread as well. I think this virus is less likely to mutate than others, although it can of course mutate as well.
(04-03-2020, 11:17 PM)danbrotherston Wrote: I am curious though, why you believe that a vaccine that is available in 18 months would take 2 years to give us herd immunity? I believe the 12-18 month estimate is for broad availability of the vaccine--and we're already 2 months into that timeline.
I think even 18 months is pretty aggressive though we might be able to pull it off in this case having started phase I trials of some candidates.